Nato's cyber-defence chief has warned that computer-based terrorism poses the same threat to national security as a missile attack.
Suleyman Anil, head of Nato's Computer Incident Response Capability Co-ordination Centre, said a determined cyberattack on a country's online infrastructure would be "practically impossible to stop".
Nations need to focus on improving their ability to quickly recover and get systems back online, an area in which nearly all countries were currently "weak", Anil told delegates at the e-Crime Congress 2008 in London.
Anil said the cyberattacks on Estonia last year, which brought down key financial and state systems, had demonstrated how cyber-terrorism could take down national infrastructure with "very serious consequences".
He said: "It stands together with air-missile defence and the global fight against terrorism."
Nato will set out an action plan for dealing with a similar infrastructure attack on one of its members at a state summit in Bucharest next month.
Anil believes the threat will continue to grow as terrorist groups become aware of the potential to cause maximum damage at minimal cost.
Anil said: "Cyber-war can become a very effective global problem because it is low-risk, low-cost, highly effective and easily globally deployable. It is almost an ideal weapon that nobody can ignore."
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Anil said attacks were becoming increasingly sophisticated, giving an example of a semi-autonomous Trojan which infiltrated Nato's open network.
He said the Trojan was scanning networks for statements on a certain underground project and then trying to implant itself on any network that mentioned it.
Nato's weapons of choice for defence purposes are off-the-shelf virus scanners, intrusion-prevention technology and forensic software, Anil said.
Countries also need to resolve issues of law enforcement across national boundaries and the technical challenges of tackling the spread of cybercrime, Anil added.
